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On the vertical structure of non-buoyant plastics in turbulent transport
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Researchers investigated how non-floating plastic debris moves through river-like flows and found that plastics settle in unique, complex patterns due to their irregular shapes. In low-turbulence conditions, interactions between the plastic particles and the riverbed enhanced mixing beyond what standard sediment transport models would predict. The study proposes a new equation for describing how plastics are distributed vertically in flowing water.
Plastic pollution is overflowing in rivers. A limited understanding of the physics of plastic transport in rivers hinders monitoring, the prediction of plastic fate and restricts the implementation of effective mitigation strategies. This study investigates two unexplored aspects of plastic transport dynamics across the near-surface, suspended and bed load layers: (i) the complex settling behaviour of plastics and (ii) their influence on plastic transport in river-like flows. Through hundreds of settling tests and thousands of 3D reconstructed plastic transport experiments, our findings show that plastics exhibit unique settling patterns and orientations, due to their geometric anisotropy, revealing a multimodal distribution of settling velocities. In the transport experiments, particle-bed interactions enhanced mixing beyond what established turbulent transport theories (Rouse profile) could predict in low-turbulence conditions, which extends the bed load layer beyond the classic definition of the bed load layer thickness for natural sediments. We propose a new vertical structure of turbulent transport equation that considers the stochastic nature of heterogeneous negatively buoyant plastics and their singularities.
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Modeling the settling and resuspension of microplastics in rivers: Effect of particle properties and flow conditions
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Researchers developed a mathematical model to simulate how microplastics of different shapes settle and resuspend in rivers, moving beyond the common assumption that all particles are spherical. They found that turbulence has a complex effect, sometimes keeping particles suspended longer and sometimes accelerating their settling, depending on flow conditions. The model reveals that particle shape significantly influences where microplastics end up in river systems.
Effects of hydrodynamics on the cross-sectional distribution and transport of plastic in an urban coastal river.
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This study investigated how river flow dynamics and plastic particle properties affect where plastics end up in river cross-sections. Researchers found that turbulence, particle density, and size all influence whether plastics float at the surface, suspend in the water column, or sink to the riverbed. Understanding these transport mechanisms is essential for accurately modeling how plastics ultimately reach the ocean.
Settling velocity of irregularly shaped microplastics under steady and dynamic flow conditions
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The settling velocities of irregularly shaped microplastics were measured under both still water and dynamic flow conditions, finding that shape strongly affected settling speed and that turbulence caused non-spherical particles to orient and settle differently than spheres, with implications for predicting microplastic vertical transport in rivers and coastal waters.
Microplastic dynamics within turbulence for improved modelling and monitoring strategies
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This study developed improved models for predicting microplastic distribution and transport within river systems, accounting for turbulence effects and the exchange between suspended load and bedload. The authors identified that existing sediment transport models fail to capture the behavior of low-density plastic particles in turbulent flow. More accurate models are needed to predict where microplastics accumulate in rivers and estimate their flux to the ocean.
Plastic drift : Mapping the course of microplastic transport in turbulent riverine flows.
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Researchers conducted laboratory experiments tracking the 3D trajectories of 24 negatively buoyant microplastic particles spanning a range of sizes, shapes, and densities in turbulent open channel flow, generating 720 trajectories to evaluate how well conventional sediment transport models apply to microplastics. Results revealed that the inherent variability in microplastic physical properties challenges direct application of sediment transport concepts to microplastic fate prediction in rivers.
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When a large batch of papers lands in the Atlas, we read through it and send a short write-up of what stood out.